A magnetic recording medium of the type produced by the process of this invention comprises a nonmagnetizable support having coated thereon a layer of a magnetic coating composition composed of a ferromagnetic material and a nonmagnetizable binder, said ferromagnetic material comprising platelet-form ferromagnetic particles having the axis of easy magnetization perpendicular to the plane of the platelet-form particle. As such ferromagnetic materials, there are known, for example, barium ferrite; barium ferrite having a part of the barium and/or iron substituted by other metals such as calcuim, strontium, lead, cobalt, nickel, etc.; MnBi; and MnBi having the manganese or bismuth thereof substituted by selenium or other metals.
In the production of such a magnetic recording medium, a process is usually employed wherein, after coating a magnetic coating composition on a nonmagnetic support, the magnetic particles in the coated layer are oriented to the recording direction in a magnetic field before drying the magnetic layer to improve the magnetic conversion characteristics for that direction; such an orientation process is already known for acicular .gamma.-Fe.sub.2 O.sub.3, etc., which is used for ordinary magnetic recording tapes and has been practically used. Examples of the orientation technique are described in, for example, Japanese Patent Publication Nos. 5350/1965; 23,624/1965; 23,626/1965; 2065/1966 and 21,251/1968.
In the present invention, it is intended to improve upon the process described in Japanese Patent Publication No. 856/1981 for providing a magnetic recording medium suitable for magnetic recording utilizaing the perpendicularly magnetizable component of platelet-form ferromagnetic particles having a magnetic anisotropy in the direction perpendicular to the plane of the ferromagnetic particle by magnetically orienting the axis of easy magnetization of the platelet-form ferromagnetic particles in the direction perpendicular to the support of the magnetic recording medium.
As described in "Nikkei Electronics", pages 100-111, Aug. 7, 1978 and "IEEE Transation of Magnetics"; Vol. MAG-15, No. 6, 1561-1563 (Nov., 1979), perpendicular magnetic recording is excellent for high-recording density magnetic recording.
As processes for orienting magnetic particles in a magnetic field in the direction perpendicular to the support surface of a magnetic recording medium, there are presently proposed a process of increasing the intensity of the magnetic field perpendicular to a web surface carrying the magnetic layer coated thereon (Japanese Patent Application (OPI) No. 58,246/1982), and a process of substantially finishing drying of the coated magnetic layer in a strong magnetic field (Japanese Patent Application (OPI) No. 58,241/1982). For producing a coating-type perpendicularly magnetized magnetic recording medium, a coating composition prepared by dispersing ferromagnetic particles having platlet form and having the axis of easy magnetization in the direction perpendicular to the plane of the platelet-form ferromagnetic particles in a nonmagnetizable binder is coated on a web support, and a magnetic field is applied to the web in the direction perpendicular to the web surface to perform the magnetic orientation treatment to align the axes of easy magnetization of the foregoing platelet-form magnetic particles perpendicular to the web surface. In this case, it is preferred to dry the coated magnetic layer in a strong magnetic field applied in the direction perpendicular to the web surface in the foregoing known processes.
However, in the case of industrially performing the foregoing orientation process while continuously transporting a web having a coated magnetic layer thereon, the section of strong field application must be greatly prolonged to substantially finish drying the coated magnetic layer within the magnetic field.